Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
The operating temperature of the fuel cell is high, about 800° C. Therefore, at the time of starting operation of the fuel cell stack, it is desirable to heat the fuel cell stack to a desired temperature rapidly using a combustor. Normally, the combustor is provided on a side of the fuel cell stack where the oxygen-containing gas is supplied, or on a side of the fuel cell stack where the exhaust gas is discharged.
However, in the structure where the combustor is provided on the side where the oxygen-containing gas is supplied, the hot fuel gas produced by combustion in the combustor directly flows into the fuel cell stack. Therefore, the separators tend to be corroded easily by the hot combustion gas, and carbon in the combustion gas adheres to the separators.
In an attempt to address the problems, structure of providing the combustor on the side of the fuel cell stack where the exhaust gas is discharged may be adopted. For example, Japanese Laid-Open Patent Publication No. 5-343083 discloses a fuel cell power generation apparatus as shown in FIG. 5. The fuel cell power generation apparatus includes a reformer 1 for reforming a fuel gas to produce an anode gas containing hydrogen, a fuel cell 2 for performing power generation using the anode gas and a cathode gas containing oxygen, a catalyst combustor 3 for burning an anode exhaust gas discharged from the fuel cell 2, and a heat exchanger 4 for performing heat exchange between the anode gas having a high temperature from the reformer 1 and the fuel gas having a low temperature to be supplied to the reformer 1. All of the reformer 1, the fuel cell 2, the catalyst combustor 3, and the heat exchanger 4 are disposed in a single pressure container 5.
In the fuel cell power generation apparatus, the reformer 1 and the fuel cell 2 are connected by an anode gas line 6a such that the heat exchanger 4 is interposed between the reformer 1 and the fuel cell 2. The heat exchanger 4 and the reformer 1 are connected by a fuel gas line 6b. Further, the catalyst combustor 3 is connected to an exhaust gas outlet of the fuel cell 2 through an anode exhaust gas line 6c and a cathode exhaust gas line 6d. The reformer 1 is connected to an outlet of the catalyst combustor 3 through a combustion gas line 6e. 
Thus, a relatively large space is required for the layout of the reformer 1, the fuel cell 2, the catalyst combustor 3, and the heat exchanger 4 in the pressure container 5. As a result, the overall size of the pressure container 5 becomes large. In the presence of a large number of pipes, heat efficiency is lowered.